Piping unit for transporting fuel

ABSTRACT

Piping unit for transporting a fuel is constructed by connecting a resin tube and a connector for connecting the resin tube to a mating pipe. The connector has a connector body including a retainer holding portion and a retainer for engaging with the mating pipe. The resin tube has a multilayered construction including an inner fuel barrier layer and an outer layer covered with a protective layer. The outer layer has a small outer diameter (od) up to 6 mm, the fuel barrier layer and the outer layer have a wall-thickness (t), and a ratio of the outer diameter (od)/the wall thickness (t) is in a range of 4 to 8.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a piping unit installed between anengine and a fuel tank to transport a fuel.

2. Description of the Related Art

Recently, as a control on exhaust emissions is tighten, a fuel injectionsystem (injection system) of high fuel efficiency has been employed evenin a compact vehicle with a small engine such as mini-vehicle,two-wheeled motor vehicle, three-wheeled motor vehicle, and all-terrainvehicle (ATV).

In this fuel injection system, a fuel is prepressurized, and theprepressurized fuel is injected only when a valve of an injector (fuelinjection nozzle) is open. So, piping for transporting a fuel isrequired to have a pressure resistance of 0.25 to 0.35 MPa.

Therefore, when a rubber hose is used for piping, it is necessary toconnect the rubber hose to a mating pipe by swaging a metal fitting ontoan end portion of the rubber hose. In this case, there is a problem thatthis results in high production cost as well as troubles.

And, if the rubber hose is used, as an outer diameter of the rubber hoseis large, there is a problem that an operator is considerablyconstrained from installing a piping unit through between componentswithin a limited tight piping space.

On the other hand, a resin tube also has been conventionally used fortransporting a fuel.

When such resin tube is adapted for piping, the resin tube is used incombination with a connector (quick connector) that permits simple andquick connection with a mating pipe.

In the resin tube, it is not necessary to swage a metal fitting onto anend portion of the resin tube for connection with the mating pipe,different from the rubber hose that is used for piping.

The connector of this type is disclosed, for example, in Patent Document1 below.

FIGS. 11 and 12 show one instance of such connectors as disclosed.

In FIGS. 11 and 12, reference numeral 200 indicates a resin tube,reference numeral 202 indicates a mating pipe to be connected with theresin tube 200.

The mating pipe 202 is formed with an engaging projection (pipe-sideengaging portion) 204 projecting annularly on an outer peripheralsurface thereof.

Reference numeral 206 indicates a connector that has a connector body(here, entirely made of resin) 208, a retainer 210, a bush 214, andO-rings 212 as sealing member.

The connector body 208 includes a retainer holding portion 216 on oneend of the connector body 208 along an axial direction (a proximal endor an axially outer end of the connector body 208), and a press-fitportion 218 on the other end thereof along the axial direction (a distalend or an axially inner end thereof) as connecting portion to the resintube 200.

The press-fit portion 218 is a portion to be press-fitted orforce-fitted within the resin tube 200 in an axial direction. Thepress-fit portion 218 is formed with annular ribs 220 at a plurality ofaxially spaced positions on an outer peripheral surface thereof. Theannular rib 220 has a saw-edged cross-section and is provided with anacute angled peak.

The press-fit portion 218 is force-fitted within the resin tube 200 andthereby the connector body 208 is connected to such resin tube 200.

At that time, the annular ribs 220 formed on the outer peripheralsurface of the press-fit portion 218 bite in an inner surface of an endportion of the resin tube 200 that is diametrically expanded anddeformed by force-fitting of the press-fit portion 218, and thereby theresin tube 200 is retained and stopped for preventing withdrawal.

Meanwhile, the press-fit portion 218 is formed with an annular groovewherein an O-ring 222 is retained. The O-ring 222 provides an air-tightseal between the press-fit portion 218 and the resin tube 200.

The above retainer holding portion 216 is a portion for holding theretainer 210 while receiving the retainer 210 therein. The connectorbody 208 is connected to the mating pipe 202 via the retainer 210.

The retainer holding portion 216 is provided with a stop portion(body-side stop portion) 224 on a trailing end (proximal end or axiallyouter end) thereof for latching onto the retainer 210.

On the other hand, the retainer 210 is a resin member that is as a wholegenerally annular, and resiliently or flexibly deformable in a radialdirection.

The retainer 210 is formed with an engaging recessed portion or engagingslit portion (retainer-side engaging portion) 225 and a latching recess(retainer-side latching portion) 226. The engaging projection 204 of themating pipe 202 engages with the engaging recessed portion 225 fromradially inward or inside the retainer 210. The latching recess 226similarly fits to the stop portion 224 of the connector body 208 fromradially inward or inside the retainer holing portion 216 to stop theretainer 210 in an axial direction.

The retainer 210 is held in the retainer holding portion 216 in anaxially fixed state by latching the latching recess 226 onto the stopportion 224 of the retainer holding portion 216.

The retainer 210 further includes an inner peripheral surface thereofthat defines a tapered inner peripheral cam surface 228, and an outerperipheral surface that defines a tapered outer peripheral cam surface230.

When the mating pipe 202 is inserted inside the retainer 210 in an axialdirection, the inner peripheral cam surface 228 abuts and guides theengaging projection 204 for further axial movement. Then the innerperipheral cam surface 228 resiliently diametrically expands theretainer 210 as a whole by the cam action as the engaging projection 204moves and thereby allows passage of the engaging projection 204.

Then, as soon as the engaging projection 204 reaches a position of theengaging recessed portion 225, the retainer 210 as a whole returns toits original shape, the engaging projection 204 simultaneously is fittedor slipped in the engaging recessed portion 225 in fixed relation withone another in an axial direction.

On the other hand, when the retainer 210 is inserted in the retainerholding portion 216 of the connector body 208 in the axial direction,the outer peripheral cam surface 230 abuts the stop portion 224, therebyresiliently diametrically contracts the retainer 210 as a whole, andlatches the latching recess 226 onto the stop portion 224 withdiametrically contracting action of the retainer 210.

Meanwhile, the retainer 210 is provided with operation tabs 231 ontrailing end portions (proximal end portions or axially outer ends)thereof. The retainer 210 also may be diametrically contracted byexerting a radially inward force to the operation tabs 231.

In the connector 206, the retainer 210 is first held in the retainerholding portion 216 of the connector body 208. Then, in this state, themating pipe 202 is inserted inside the retainer 210 in the axialdirection.

During that time, the retainer 210 is resiliently expanded in adiametrically expanding direction by the engaging projection 204 of themating pipe 202. As soon as the engaging projection 204 reaches theengaging recessed portion 225, the retainer 210 diametrically contracts,and the engaging projection 204 engages in the engaging recessed portion225.

On the other hand, the retainer 210 may be first attached to the matingpipe 202. Then, in this state, the mating pipe 202 with the retainer 210thereon may be inserted in the connector body 208.

During that time, the retainer 210 diametrically contracts once, then,as soon as the latching recess 226 reaches a position of the stopportion 224, the retainer 210 diametrically enlarges to latch thelatching recess 226 onto the stop portion 224.

The bush 214 and the O-rings 212 as sealing member are placed andretained, in a distal end of the connector body 208 relative to theretainer holding portion 216. When the mating pipe 202 is insertedwithin the connector body 208, the O-rings 212, or the O-rings 212 andthe bush 214 contact air-tightly with an inserting end portion 232 ofthe mating pipe 202, namely an outer peripheral surface of a leading end(axially inner end) of the inserting end portion 232 relative to theengaging projection 204 (an outer peripheral surface of a leading endportion of the inserting end portion 232 extending from the engagingprojection 204), and provide an air-tight seal between the mating pipe202 and the connector body 208.

As shown in FIG. 11 (A), two O-rings 212 are used in the connector 206.However, as shown in FIG. 11 (B), as the case may be, single O-ring 212may be used in the connector 206 for compact sizing of the connector206.

As understood from the above, the resin tube 200 may be easily connectedwith the mating pipe 202 by use of such connector 206 with a simpleaction.

The conventional resin tube 200 here is, for example, about 6 mm in aninner diameter and about 8 mm in an outer diameter, and adapted in apiping system as shown in FIG. 13.

In this piping system, a fuel in a fuel tank 234 is transported(supplied) by a fuel pump 236 through a supply channel 238 under acertain pressure, and injected from an injector 240 to a cylinder 242 ofan engine. And, a surplus fuel is returned through a return channel 244to the fuel tank 234.

For assembling a piping system in a motor vehicle body, the resin tube200 is first formed or molded in a bent or curved shape according to apredetermined piping layout and attached with connector 206 on each ofor one of both ends of the resin tube 200. Then the resin tube 200 withconnectors 206 thereon is delivered to an assembling site and assembledin the motor vehicle body on the assembling site.

However, the bent or curved resin tube 200 is obtained, for example, inthe following steps. A straight tubular resin tube (a resin tube moldedin a straight tubular shape) is fitted in a constraining mold to retainthe resin tube in a bent or curved shape, and the resin tube as a wholeor the constraining mold is put into an oven to be heated, for example,at a temperature of 150° C. to 160° C. for 20 to 30 minutes to be formedinto a bent or curved shape, then, the constraining mold is taken outfrom the oven, cooled, and the resin tube is removed out of the mold(for example, as disclosed in Patent Document 2). However, manyproduction steps are required or exist in this production method,resulting in increase of the production cost. And, here, the resin tubes200 corresponding to the type of a motor vehicle, strictly speaking,corresponding to the type of the piping layout is required, and variedtypes of the resin tube should be produced accordingly. This is also afactor of the cost increase.

However, instead of a piping system (so-called a return fuel system)shown in FIG. 13 where a surplus fuel is returned to the fuel tank 234,another piping system, so-called returnless fuel system where a surplusfuel is not supplied but only a required quantity of the fuel, namely aquantity to be consumed is supplied from the fuel tank 234 to the enginehas been increasingly applied recent years.

In the returnless fuel system, only the required quantity of the fuel issupplied. Therefore, if the resin tube 200 with the same diameter as inthe piping system shown in FIG. 13 is used in the returnless fuelsystem, a fuel is likely accumulated. And, the fuel in accumulated stateis evaporated in the piping under a certain atmosphere in the engineroom, and resultantly, the engine revolutions are liable to be unstable.

In this case, for the resin tube 200, a small-diameter resin tube of anouter diameter up to 6 mm is preferably used in order not to causeaccumulation of the fuel.

The resin tube with such small diameter has greater flexibility than aresin tube with large diameter. So, inventors of the present inventiondevised an assembling structure of a resin tube where the resin tube isnot initially formed or molded in a bent or curved shape. The resin tubeis formed or molded in a straight tubular shape and attached with aconnector on each of or one of the both end portions thereof. Then, theresin tube equipped with the connectors or the connector thereon isdelivered in an assembling site, and assembled for piping in a motorvehicle body by bending or curving the resin tube.

In this manner, a cost related to the resin tube may be lowered. And itbecomes possible to use a common type of resin tube for various types ofmotor vehicles or various piping layouts in a versatile manner.

This assembling mode does not apply only to the resin tube with smalldiameter, but applies to resin tubes with relatively large diameter andexcellent flexibility.

However, there is a problem that once a resin tube is broken (kinked)during assembly, the resin tube never returns to normal state and isnever usable any more. So, in case where a resin tube is adapted fortransporting a fuel, it is required that the resin tube is hard to bebroken (buckled or kinked) when bent or curved.

By the way, such connector as described in Patent Document 3 may be usedto be attached to an end portion of the resin tube 200. This connector300 is, as shown in FIGS. 14 and 15, configured such that a relativelythin-walled retainer 302 is mounted on a retainer holding portion 304 ina direction perpendicular to an axis.

The connector 300 has a connector body (here, entirely made of resin)306 in the form of a tubular shape as a whole, a retainer 302, O-rings308 as sealing member and a bush 310 (refer to FIG. 14 (A)).

The connector body 306 includes a short cylindrical retainer holdingportion 304 on one end of the connector body 306 along an axialdirection and a connecting portion 312 on the other end thereof alongthe axial direction, for example, as connecting portion to the resintube 200.

The retainer 302 in the form of a looped shape is configured byconnecting a pair of engaging portions (retainer-side engaging portions,retainer-side latching portions) 314 integrally to V-shaped bodies 316at one and the other ends of the engaging portions 314, respectively(refer to FIG. 14 (B). The retainer 302 is inserted in the retainerholding portion 304 via an opening 318 of the retainer holding portion304 by narrowing a width of the retainer 302, and then the retainer 302is returned to its original width (namely its original shape) in theretainer holding portion 304. The retainer 302 is located therein withits original shape.

When a mating pipe 202 (in the form of slightly different shape from themating pipe 202 shown in FIG. 11) is inserted in the retainer 302, theengaging projection 204 of the mating pipe 202 abuts slant guidesurfaces or slant guide cam surfaces 320 of the engaging portions 314.Then the engaging projection 204 pushes the slant guide cam surfaces 320radially outwardly, and advances while widening the retainer 302. Assoon as the engaging projection 204 passes through the engaging portions314, the retainer 302 is slightly narrowed so that the engaging portions314 engages with the engaging projection 204 in an axial direction(refer to FIG. 15). Here, the engaging portions 314 enter cutoutportions (body-side stop portions) 322 of the retainer holding portions304 and engage with the retainer holding portion 304 in the axialdirection. In this manner, the mating pipe 202 and the retainer 302 orthe connector body 306 are securely fixed in the axial direction. And,the mating pipe 202 may be pulled out of the connector 300 by pressingpress portions 324 of the retainer 302 radially inwardly, and therebywidening a distance between the engaging portions 314. As shown in FIG.16, in some case, enclosing portions 326 are formed in the opening 318so as to rise radially outwardly in order not to allow the pressportions 324 to protrude outwardly.

Or, a connector as shown in Patent Document 4 may be also used. Thisconnector 400 is, as shown in FIGS. 17 and 18, configured such that aretainer 402 of a horse-shoe shape is mounted on a retainer holdingportion 404 in a direction perpendicular to an axis. The connector 400is provided further with a checker member 406 for verifying connectionto the mating pipe 202.

The connector 400 has a connector body (here, entirely made of resin)408 in the form of a cylindrical shape as a whole, a retainer 402,O-rings 410 as sealing member, a bush 412 and the checker member 406(refer to FIGS. 17 and 18(B)).

The connector body 408 includes a short tubular retainer holding portion404 on one end of the connector body 408 along an axial direction and aconnecting portion 414 on the other end thereof along the axialdirection, for example, as connecting portion to the resin tube 200.

The checker member 406 is shaped a box and includes a pair of resilientarms 416 and stop recesses 418 on end portions of the resilient arms416. The checker member 406 is installed on an outer periphery of theretainer holding portion 404 in a direction perpendicular to an axis andis located in the retainer holding portion 404 so as to engage the stoprecesses 418 with bottom surface portions 420, respectively.

The retainer 402 includes a pair of detecting lugs 422 and detectingdetents 424 on end portions (free end portions) of the detecting lugs422, and the detecting detents 424 protrude radially inwardly. Theretainer 402 is mounted on an outer periphery of the retainer holdingportion 404 in the direction perpendicular to the axis and is located inthe retainer holding portion 404 so as to protrude the detecting detents424 inside a passage of the engaging projection 204 of the mating pipe202 (refer to FIG. 18 (A)).

When the mating pipe 202 is inserted in the connector body 408, theengaging projection 204 advances with pushing away slant guide surfacesor slant guide cam surface 425 and abuts the bush 412 (namely, themating pipe 202 is correctly connected to the connector body 408), thedetecting detents 424 of the retainer 402 are pushed and moved radiallyoutwardly by the engaging projection 204, engagement of the detectingdetents 424 and dents 430 of receiving slots 428 is cancelled, andthereby the retainer 402 is allowed to be further pushed in thedirection perpendicular to the axis. When the retainer 402 is furtherpushed in the direction perpendicular to the axis, engaging portions(retainer-side engaging portions) 431 of the retainer 402 engage withthe engaging projection 204 of the mating pipe 202, and simultaneously,the resilient arms 416 of the checker member 406 are moved by guide lugs432 of the retainer 402, the stop recesses 418 of the resilient arms 416are pushed radially outwardly, and thereby engagement of the stoprecesses 418 and the bottom surface portions 420 is cancelled. In thismanner, the mating pipe 202 and the connector body 408 are securelyfixed together in the axial direction. In this securely fixed relation,the checker member 406 is allowed to separate from the connector body408. That is, only when the mating pipe 202 is connected to theconnector 400 correctly, the checker member 406 can be removed from theconnector body 408. Meanwhile, the retainer 402 engages with restrainingflanges 434, 436, 438 (body-side stop portions) of the connector body404 at a rear end surface, middle recessed portions and a front endsurface (retainer-side engaging portions) of the retainer 402 in anaxial direction. Patent Document 1 JP-A, 11-201355 Patent Document 2JP-A, 6-190913 Patent Document 3 JP-B, 2641683 Patent Document 4 JP-A,2004-251319

SUMMARY OF THE INVENTION

Under the circumstances described above, it is an object of the presentinvention to provide a novel piping unit having a resin tube as anessential element. For example, the piping unit can be easily connectedto a mating pipe without need of metal fittings to be swaged forconnecting to the mating pipe during assembly of the piping unit to amotor vehicle body. And, for example, the resin tube is hard to bebroken when a bending force is exerted thereto.

A piping unit according to the present invention is arranged between anengine and a fuel tank for transporting a fuel. The piping unitcomprises a resin tube as an essential element for the piping unit, anda connector attached to an end portion of the resin tube for connectingthe resin tube to a mating pipe. The connector has a connector bodyincluding a retainer holding portion on a proximal end (one end along anaxial direction) of the connector body and a tube connecting portion ora connecting portion on a distal end (the other end along the axialdirection) of the connector body for connecting to the resin tube, aretainer held in or on the retainer holding portion for engaging withthe mating pipe to securely fix the connector body in the axialdirection, and a sealing member contacting air-tightly with an outerperipheral surface of the mating pipe to provide a seal between theconnector body and the mating pipe. The resin tube has a multilayeredconstruction including an inner fuel barrier layer and an outer layermade of polyamide (PA) covered further with a protective layer on anouter peripheral surface or an outer side of the outer layer. The resintube inside the protective layer (the resin tube excluding theprotective layer, or a tube body excluding the protective layer from theresin tube) has a small outer diameter (od) up to 6 mm and a wallthickness (t), and a ratio of the outer diameter (od) to the wallthickness (t) (wall-thickness ratio), namely the outer diameter (od)/thewall thickness (t) of the resin tube inside the protective layer is in arange of 4 to 8.

The connector body may be provided, for example, with a socket likeretainer holding portion on one end along an axial direction or one endportion along the axial direction, and a connecting portion forconnecting to a resin tube on the other end or the other end portion.

For example, the fuel barrier layer may be made ofethylene-tetrafluoroethylene (ETFE).

For example, a main constituent of the fuel barrier layer may be amaterial selected from a group consisting ofethylene-tetrafluoroethylene (ETFE), thermoplastic polyester elastomer(TPEE), polybutylene terephtharate (PBT), polybutylene naphthalate(PBN), polyphenylene sulfide (PPS), polyethylene (PE), polypropylene(PP), polyvinylidene fluoride (PVDF), and polyethylene vinyl alcohol(EVOH).

For example, the resin tube may be attached to the connectors at bothend portions of the resin tube by force-fitting or press-fitting, orsolvent welding.

For example, a checker member may be formed or mounted on the connector.The checker member may be configured removable, namely may bedisengageable from the connector when the mating pipe is connected tothe connector correctly.

For example, a closing member may be mounted on the connector forclosing a connecting opening thereof before the mating pipe is connectedto the connector.

For example, the piping unit may be used for piping in a returnless fuelsystem in which the fuel is supplied from the fuel tank to an injectorof the engine, but is not returned from the injector to the fuel tank.

As stated above, according to the present invention, the piping unit isconstructed by combining a connector with a resin tube including aninner fuel barrier layer and an outer layer of PA. The outer layer of PAis covered with a protective layer. The connector is adapted forconnecting the resin tube with a mating pipe, and has a connector body,a retainer and a sealing member. The resin tube inside the protectivelayer (a tube or tube body excluding the protective layer from the resintube) has a small outer diameter (od) up to 6 mm, and a ratio of theouter diameter (od) of the resin tube (the tube or tube body excludingthe protective layer from the resin tube)/a wall thickness (t) of theresin tube (the tube or tube body excluding the protective layer fromthe resin tube) is in a range of 4 to 8. According to the piping unit ofthe present invention, an operator can easily connect the mating pipeand the resin tube by means of a connector with a little labor. And, aswill be described later, even if a bending force is exerted on the resintube, the resin tube can be effectively prevented from being broken bylimiting the ratio of the outer diameter (od) to the wall-thickness (t)within the above range (4 to 8). So, the operator can easily assemblethe piping unit in a motor vehicle body while bending the resin tube.

Specifically, the operator has to securely fix the resin tube to themotor vehicle body with a fixing clamp while bending the resin tubeaccording to a predetermined piping layout, through between variouscomponents equipped in the motor vehicle body, within a narrow, limitedpiping space. At that time, in some case, the resin tube is securelyfixed by the fixing clamp while changing the resin tube from a gentlebent shape to a steep bent shape, namely changing a curvature of theresin tube from a large radius shape to a small radius shape. And, insome case, on the contrary, the resin tube is securely fixed whilechanging the resin tube or loosening a bent shape of the resin tube froma small radius shape to a large radius shape. If both of the pipingmanners is adaptable in assembling a piping unit to a motor vehiclebody, the operator can easily install the piping unit, namely the resintube along a piping route.

For that purpose, it is preferred that the resin tube is not broken(buckled, kinked) while the resin tube is bent at a predeterminedcurvature radius, specifically at curvature radius (R) up to 50 mm, ormore preferably at curvature radius (R) up to 30 mm.

It is confirmed that when the resin tube has a ratio of the outerdiameter (od) to the wall-thickness (t) (wall-thickness ratio), namelythe outer diameter (od)/the wall thickness (t) within a range of 4 to 8according to the present invention, the resin tube may be favorablyarranged and assembled while being bent, without causing such breakage.

Therefore, a piping unit according to the present invention, which isconstructed in combination of a resin tube and a connector, may beeasily assembled in a motor vehicle body.

Here, the retainer to be installed on the connector or the connectorbody is formed separately from the connector body or unitary with theconnector body, and is configured to be resiliently or flexiblydeformable in a radial direction. The retainer may have a retainer-sidelatching portion. The retainer may also have a cam surface (guidesurface or abutment surface) or an inner peripheral cam surface (innerperipheral guide surface or inner peripheral abutment surface) forresiliently diametrically expanding the retainer at insertion of amating pipe in the retainer, and/or a cam surface (guide surface orabutment surface) or an outer peripheral cam surface (outer peripheralguide surface or outer peripheral abutment surface) for resilientlydiametrically contracting the retainer at insertion of the retainer inthe retainer holding portion. For example, the retainer-side latchingportion is latched onto and securely fixed to a body-side stop portionin an axial direction by fitting on the body-side stop portion, forexample, from radially inward or inside the retainer holding portion.The body-side stop portion is formed, for example, on a side of theretainer holding portion.

According to the present invention, the resin tube is a small-diametertube with outer diameter up to 6 mm, and has a high flexibility. Asdescribed above, thanks to the flexibility, the operator can easilyassemble a piping unit in the motor vehicle body according to apredetermined piping layout with use of fixing clamps while bending theresin tube. And, by limiting a relationship of the outer diameter (od)to the wall-thickness (t) of the resin tube within the above range, itmay be prevented, for example, that the resin tube is broken when thepiping unit is assembled.

According to the present invention, for example, fluorine resin such asETFE may be used for the above fuel barrier layer. The fluorine resin isexcellent in a fuel barrier property and processability, therefore,suitable for the fuel barrier layer.

Here, the fuel barrier property means impermeability to a fuel(gasoline) and resistance to inferior gasoline (inferior gasoline isgasoline mixed with ethanol, methanol, toluene or the like that causes acrack in an inner surface of a resin tube).

Or, the fuel barrier layer may be made by using a material selected froma group consisting of ETFE, TPEE, PBT, PBN, PPS, PE, PP, PVDF, and EVOHas a main constituent, and satisfactory or sufficient effects may beexpected also in such fuel barrier layer.

In the present invention, for example, the above resin tube may beattached to the connectors at both end portions of the resin tube byforce-fitting, press-fitting or solvent welding.

In this case, it is not necessary to swage a metal fitting or the likeon the resin tube for connecting the resin tube with the mating pipe.This allows the operator to connect the resin tube with the mating pipevery easily without difficulty in a limited tight space.

And, according to one aspect of the present invention, a checker membermay be formed or mounted in or on the connector. The checker isconfigured removable or disengageable from the connector when the matingpipe is connected to the connector correctly.

In this configuration or aspect, it is not necessary to verifyconnection of the connector with the mating pipe visually or by visualobservation. and it is possible to verify its connection by removing thechecker member from the connector or collecting the checker members.Here, even in case where connecting work is done for a place beyond theoperator's view such as a remote part in the motor vehicle body, theoperator can easily verify a correct connection.

According to one aspect of the present invention, a closing member maybe mounted in the connector for closing a connecting opening of theconnector before the mating pipe is connected to the connector. In thismanner, it may be favorably prevented by the closing member that dust orother foreign substance enters inside the resin tube through theconnector.

Here, the connectors may be attached to both end portions of the resintube, and the closing member may be mounted in each of the connectors.And, when one closing member is removed from one of the connectors onboth ends of the resin tube and only the other closing member is left onthe other of the connectors, the operator can easily verify whetherthere is leakage at a joint area (connecting area) between the connectorand the resin tube or in the piping unit by exerting a pressure insidethe resin tube through an open end of the one connector.

The piping unit of the present invention is specifically suitable forpiping in a returnless fuel system in which the fuel is supplied from afuel tank to an injector of an engine, but is not returned from theinjector to the fuel tank.

Further, for the resin tube of the present invention, a small diameterresin tube with outer diameter up to 6 mm is adapted. When such smalldiameter tube is used for piping of a returnless fuel system, a flowvelocity of transporting fluid does not become slow. This restrains atemperature increase of a fuel fluid inside the resin tube. Therefore,the resin tube of the present invention is suitably adapted for pipingof the returnless fuel system.

Now, the preferred embodiments wherein the present invention is adaptedfor a piping unit to be arranged between an engine and a fuel tank in acompact vehicle for transporting a fuel will be described in detail withreference to the drawings.

Here, the compact vehicle means specifically a two-wheeled motorvehicle, a three-wheeled motor vehicle, and all-terrain vehicle (ATV) orthe like, or a mini-vehicle.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 (A) is a view showing a piping unit according to one embodimentof the present invention in an assembled state in a motor vehicle body.

FIG. 1 (B) is an enlarged view of a part B of FIG. 1 (A).

FIG. 2 (A) is a partly exploded sectional view of a connector in the oneembodiment.

FIG. 2 (B) is a sectional view showing a state that a resin tube or thepiping unit is connected with a mating pipe by means of the connector.

FIG. 3 is a view of a fixing clamp in the one embodiment.

FIG. 4 (A) is a perspective view showing a state that the resin tube isfastened by the fixing clamp.

FIG. 4 (B) is a sectional view showing the state that the resin tube isfastened by the fixing clamp.

FIG. 5 (A) is a view showing the piping unit of the one embodiment in astate before assembled in the motor vehicle body.

FIG. 5 (B) is a sectional view taken along B-B line in FIG. 5 (A).

FIG. 6 is an exploded perspective view of a relevant part of FIG. 5 (A).

FIG. 7 is a sectional view of the relevant part of FIG. 5 (A).

FIG. 8 is a sectional view taken along A-A line in FIG. 7.

FIG. 9 (A) is an explanatory view of an action when the mating pipe isconnected to the connector, and showing a state just before the matingpipe is inserted in the connector.

FIG. 9 (B) is an explanatory view of an action when the mating pipe isconnected to the connector, and showing a state that the mating pipe isinserted in the connector.

FIG. 9 (C) is an explanatory view of an action when the mating pipe isconnected to the connector, and showing a state that an engagingprojection of the mating pipe abuts a latching claw of a checker member.

FIG. 9 (D) is an explanatory view of an action when the mating pipe isconnected to the connector, and showing a state that the checker memberis disengaged from the connector.

FIG. 10 is a view showing a relationship between a bend R and a wallthickness ratio of the resin tube in the one embodiment according to thepresent invention.

FIG. 11 (A) is a view showing a conventional example of connection of apiping unit by means of a connector.

FIG. 11 (B) is a view showing an example where single O-ring is used inthe connector of FIG. 11 (A).

FIG. 12 (A) is a view of a relevant part of the connector of FIG. 11along with a resin tube, and showing a state before the connector isforce-fitted in the resin tube.

FIG. 12 (B) is a view of the relevant part of the connector of FIG. 11along with the resin tube, and showing a state that the connector isforce-fitted in the resin tube.

FIG. 13 is a schematic view of a return fuel system.

FIG. 14 (A) is a sectional view of another connector.

FIG. 14 (B) is a view showing a retainer of the another connector.

FIG. 15 is a sectional view showing a state that the another connectoris connected to a mating pipe.

FIG. 16 is another sectional view showing the state that the anotherconnector is connected to the mating pipe.

FIG. 17 is an exploded perspective view of yet another connector.

FIG. 18 (A) is a sectional view of the yet another connector.

FIG. 18 (B) is a sectional view showing a state that the yet anotherconnector is connected to a mating pipe.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to FIG. 2 (B), reference numeral 10 is a mating pipe thatis formed integrally to a component such as an engine or a fuel tanksecurely fixed to a motor vehicle body. The mating pipe 10 is formedwith an engaging projection (pipe-side engaging portion) 12 projectingannularly on and around an outer peripheral surface thereof.

FIG. 5 (A) shows piping unit 13 in a state before assembled in the motorvehicle body. In Figures, reference numeral 14 indicates a resin tube,reference numeral 16 indicates a connector (quick connector). Theconnectors 16, 16 are attached to both end portions of the resin tube14. However, when the resin tube 14 is connected directly to a matingmember such as the mating pipe 10 on one end portion of the resin tubeby force-fitting or the like, the connector 16 is attached only to theother end portion of the resin tube 14.

Here, the resin tube 14 has a straight tubular shape before assembled inor to the motor vehicle body. That is, the resin tube 14 is formed ormolded in the straight tubular shape.

Meanwhile, the piping unit 13 is adaptable for a returnless fuel systemand for another fuel system where a surplus gasoline is returned to afuel tank (return fuel system), and specifically suitable for theformer, the returnless fuel system.

As shown in FIG. 5 (B), the resin tube 14 has a multilayeredconstruction that includes a layer of fluorine resin as an inner fuelbarrier layer, concretely, a layer 14A of ETFE and an outer layer 14B ofPA 12. A protective layer 15 is laminated on an outer peripheral surfaceof the outer layer 14B in a coating manner along an entire length of theouter layer 14B. The protective layer 15 is made of rubber (here,ethylene propylene diene rubber (EPDM)) to protect the resin tube 14 orthe outer layer 14B and prevent the resin tube 14 or the outer layer 14Bfrom being damaged at a portion clamped by a fixing clamp 48 (refer toFIGS. 1, 3 and 4) that will be described later.

In addition, following materials may be used aside from ETFE for a fuelbarrier layer 14A. Namely, as for fluorine resin other than ETFE, forexample, usable are polyvinylidene-fluoride (PVDF), polyvinyl fluoride(PVF), polychlorotrifluoroethylene (CTFE),ethylene-chlorotrifluoroethylene copolymer (ECTFE),ethylene-tetrafluoroethylene-hexafluoropropylene copolymer,hexafluoropropylene-tetrafluoroethylene copolymer (FEP),polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkoxyvinyl ether copolymer (PFA),tetrafluoroethylene-hexafluoropropylene-perfluoroalkoxy ethyleneterpolymer, vinylidene fluoride-tetrafluoroethylene copolymer,vinylidene fluoride-hexafluoropropylene copolymer,tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride terpolymer(THV), hexafluoropropylene-perfluoroalkoxy vinyl ether, vinylidenefluoride-chlorotrifluoroethylene copolymer, vinylidenefluoride-perfluoroalkoxy vinyl ether, vinylidenefluoride-tetrafluoroethylene-perfluoroalkoxy vinyl ether, vinylidenefluoride-hexafluoropropylene-perfluoroalkoxy vinyl ether,ethylene-tetrafluoroethylene-perfluoroalkoxy vinyl ether,ethylene-hexafluoropropylene-perfluoroalkoxy vinyl ether,ethylene-tetrafluoroethylene-hexafluoropropylene-perfluoroalkoxy vinylether, or the like. However, specifically, ETFE is suitable in view oftube processability, etc.

The above fuel barrier layer 14A may include the above material as mainconstituent. Besides the above, the fuel barrier layer 14A is preferablymade by using a main constituent selected from a group consisting ofthermoplastic polyester elastomer (TPEE), polybutylene terphthalate(PBT), poly-phenylene sulfide (PPS), polyethylene (PE), polypropylene(PP), polybutylene napthalate (PBN), a polyvinylidene fluoride (PVDF),and ethylene-vinyl alcohol copolymer (EVOH).

Or, an alloy material made by using any of these resins as mainconstituent and improving conductivity, flexibility, shock resistance,etc. may be used for the fuel barrier layer.

In this embodiment, the resin tube 14 is a small diameter tube that hasan inner diameter (id) of 2.5 mm, an outer diameter (od) of the outerlayer 14B of 4 mm.

Here, the ETFE layer 14A has the inner diameter (id) of 2.5 mm and awall thickness of 0.2 mm, the PA layer 14B has a wall thickness of 0.55mm, and the protective layer 15 has a wall thickness of 1.0 mm. Namely,a total of wall-thickness (t) of the ETFE layer 14A as an inner layerand the PA layer (outer layer) 14B is 0.75 mm.

The resin tube 14 is designed to have an overall length L of 200 to 1500mm.

However, the multilayered construction, material and dimension such aswall thickness and length are given by way of example. Needless to say,these may be modified variously.

As shown in FIG. 2, the connector 16 has a connector body (here,entirely made of resin) 18 of a tubular shape as a whole, a retainer 20,a bush 24 and O-rings 22, 22 as sealing member (also refer to FIG. 6).For example, the O-ring 22 functions as sealing member, while the bush24 functions not as sealing member but as stop against lateral wobblingwith respect to an axis.

In this embodiment, the connector 16 is made of PA (except the sealingmember). However, the material for the connector 16 is selectablesuitably in view of heat resistance, fuel impermeablity, gasolineresistance (resistance to swelling in gasoline) and cost.

Specifically, polyamide type (PA11, PA12, P6, PA66, polyphtalamide(PPA), etc.) and polyphenylene sulphide (PPS) or the like are excellentin heat resistance, and polyester type (polybutylene terephthalate(PBT), polyethylene terephthalate (PET), polyethylene naphthalate (PEN),etc.) is excellent in fuel impermeability and resistance to gasoline.

And, polyacetal (POM) is available at relatively low cost while securingheat resistance, fuel impermeability, and resistance to gasoline.

And, glass fiber may be added in the above materials to enhance strengthor nanocomposite material such as clay may be added in the abovematerials to improve the fuel impermeability.

These materials are also suitable for a material for the resin tube 14.For the material of the resin tube 14, an alloy of elastomer and one ofthese resin materials may be used. Such alloy may provide the resin tube14 with flexibility in addition to heat resistance and fuelimpermeability inherent in resin itself.

The above connector body 18 has a socket like retainer holding portion26 on an proximal end thereof and a press-fit or force-fit portion(nipple portion) 28 on a distal end thereof as a connecting portion tothe resin tube 14, as shown in FIG. 2.

The retainer holding portion 26 is a portion for receiving and holdingthe retainer 20 therein. The connector body 18 is connected to themating pipe 10 via the retainer 20.

The retainer holding portion 26 is formed with a pair of opening windows30, 30 and stop portions (body-side stop portions) 32, 32 on a trailingend thereof for being latched in the retainer 20. The pair of openingwindows 30, 30 are disposed in a diametrically symmetrical positionswith each other.

And, the retainer 20 is a member of generally annular shape (here,C-shape in section) as a whole and made of resin. The retainer 20 isdesigned resiliently and flexibly deformable in a radial direction.

The retainer 20 has engaging recessed portions or engaging slit portions(retainer-side engaging portions) 34, 34 and latching recesses(retainer-side latching portions) 36, 36. The engaging projection 12 ofthe mating pipe 10 engages with the engaging recessed portion 34 fromradially inward or inside the retainer 20 to be securely fixed in anaxial direction, while the latching recess 36 similarly fits to orlatches onto the stop portion 32 of the connector body 18 from radiallyinward or inside the retainer holding portion 26 to stop the retainer 20in the axial direction.

The retainer 20 is held by the retainer holding portion 26 in fixedrelation in the axial direction while latching the latching recess 36onto the stop portion 32 of the retainer holding portion 26.

The retainer 20 further includes an inner peripheral surface thatdefines a tapered inner peripheral cam surface or tapered innerperipheral guide surface 38, and an outer peripheral surface thatdefines a tapered outer peripheral cam surface or tapered outerperipheral guide surface 40.

The inner peripheral cam surface 38 abuts the engaging projection 12,and guides the engaging projection 12 for axial movement when the matingpipe 10 is inserted inside the retainer 20 in the axial direction. Asthe engaging projection 12 moves, the inner peripheral cam surface 38resiliently diametrically enlarges the retainer 20, for example, as awhole under camming action or guiding action so as to allow passage ofthe engaging projection 12.

Then, as soon as the engaging projection 12 reaches a position of theengaging recessed portion 34, the retainer 20 returns to its originalshape as a whole, and simultaneously, the engaging projection 12 isfitted in the engaging recessed portions 34, 34 in fixed relation withone another in an axial direction.

On the other hand, when the retainer 20 is inserted in the retainerholding portion 26 of the connector body 18 in the axial direction, theouter peripheral cam surface 40 abuts the stop portions 32, 32, therebyresiliently diametrically contracts the retainer 20, for example, as awhole, and finally latches the latching recesses 36, 36 onto the stopportions 32, 32, respectively.

The retainer 20 includes operation tabs 42, 42 on trailing end portions(proximal end portions or axially outer ends) thereof. The retainer 20may also be diametrically contracted by exerting a force to theoperation tabs 42, 42 radially inwardly.

In the connector 16, the retainer 20 is first held in the retainerholding portion 26 of the connector body 18, and in this state, themating pipe is inserted inside the retainer 20 in the axial direction.

During that time, the retainer 20 is resiliently expanded in adiametrically expanding direction by the engaging projection 12 of themating pipe 10. And, as soon as the engaging projection 12 reaches theengaging recessed portions 34, 34, the retainer 20 diametricallycontracts and the engaging projection 12 engages in the engagingrecessed portion 34.

Alternatively, the retainer 20 is first attached to the mating pipe 10,and in this state, the mating pipe 10 with the retainer 20 thereon maybe inserted in the connector body 18.

At that time, the retainer 20 once diametrically contracts, and then, assoon as the latching recess 36 reaches positions of the stop portions32, 32, the retainer 20 diametrically expands and the latching recess 36latches onto the stop portions 32, 32.

The bush 24 and the above O-rings 22, 22 as the sealing member areequipped and held inside a distal end or leading end of the connectorbody 18 relative to the retainer holding portion 26. As soon as themating pipe 10 is inserted in the connector body 18, the O-rings 22, 22or the O-rings 22, 22 and the bush 24 contact air-tightly an insertingend portion 44 of the mating pipe 10, namely an outer peripheral surfaceof a leading end of the inserting end portion 44 relative to theengaging projection 12 (or an outer peripheral surface of a leading endof the mating pipe 10 extending from the engaging projection 12 in aleading direction (traveling direction) of the mating pipe 10) toprovide an air-tight seal between the mating pipe 10 and the connectorbody 18.

The force-fit portion 28 is a portion to be force fitted or press fittedinside the resin tube 14 in the axial direction. The force-fit portion28 is formed with annular ribs 46 at a plurality of axially spacedpositions on an outer peripheral surface thereof. The annular rib 46 hasa saw-edged cross-section and is provided with an acute angled peak.

The connector body 18 is stopped relative to the resin tube 14 by forcefitting the force-fit portion 28 in an end of the resin tube 14.

FIGS. 1 (A) and 1 (B) show a state that the above piping unit 13 isassembled in a motor vehicle body.

As shown in the figures, here, the resin tube 14 is bent or curved inarcuate shape at a plurality of points (here, three bent points 50-1,50-2, 50-3 are shown) along a longitudinal direction based on itsflexibility. Both side portions of each of the plurality of the bentpoints 50-1, 50-2, 50-3 are held and fastened to the motor vehicle bodyby fixing clamps 48, 48.

In this manner, the resin tube 14 with connectors 16, 16 thereto isentirely provided with bends or bent portions as predetermined. And theresin tube 14 in this state is assembled in the motor vehicle body whilebeing connected with the mating pipes 10 via the connectors 16, 16.

That is, the resin tube 14 that is initially formed in straight tubularshape is arranged and assembled in the motor vehicle body while beingrestrained and retained in bent shape as desired by the fixing clamps48, 48.

FIGS. 3 and 4 show a preferred embodiment of the fixing clamp 48. Here,FIG. 3 shows the fixing clamp 48 before fixed to the motor vehicle body,while FIG. 4 shows the fixing clamp 48 after fixed thereto.

In FIG. 3, the fixing clamp 48 is made of resin, and is flexible orresilient. The fixing clamp 48 has a holding portion 54 and a mountingportion 56. The holding portion 54 is formed in annular shape as awhole, and provided with an opening 52 in a predeterminedcircumferential position thereof. The holding portion 54 includes a pairof guide duck bill portions 53, 53 projecting outwardly, on both ends ofthe opening 52. Thereby the holding portion 54 is in a form of generallyC-shape. The mounting portion 56 has an insert portion 59 for a holdingbore 57 in a panel of a side of the motor vehicle, and a pair ofpinching portions 61A, 61B for pinching the panel from inside andoutside the panel. The pinching portion 61A is formed integrally on anouter end portion of the mounting portion 56 or the insert portion 59(an end portion of the mounting portion 56 or the insert portion 59 nearthe holding portion 54) so as to extend in both lateral directions (bothlaterally outward directions, in right and left directions in FIG. 3),while the pinching portion 61B is formed integrally on an inner endportion of the mounting portion 56 or the insert portion 59 (an endportion of the mounting portion 56 or the insert portion 59 opposite tothe holding portion 54) so as to extend in the both lateral directions.The pinching portion 61B integrally includes foot portion 61B-1 thatextends laterally outwardly and is angled toward the holding portion 54on both lateral sides, and turned-back portion 61B-2 that extends inlaterally inward directions from laterally outer ends of the footportion 61B-1 and is angled toward the holding portion 54. A distancebetween laterally outer ends of the pinching portion 61A is sufficientlygreater than a width of the holding bore 57, and a distance betweenlaterally outer ends of the pinching portion 61B (a distance betweenlaterally outer ends of the foot portion 61B-1) is slightly greater thanthe width of the holding bore 57.

As shown in FIG. 4 (A), in the fixing clamp 48, the resin tube 14 isslipped in the holding portion 54 via the opening 52 in a directionperpendicular to an axis while resiliently widening the holding portion54, and thereby the resin tube 14 is held by the holding portion 54.Then the fixing clamp 48 is securely fixed to the motor vehicle body inthe holding bore 57, and thereby the resin tube 14 is in fixed relationto the motor vehicle body. The fixing clamp 48 is securely fixedthereto, for example, in a following manner. The insert portion 59 isinserted in the holding bore 57 of a panel such that the pinchingportion 61B is force-fitted within the holding bore 57 while beingnarrowed or deformed laterally inwardly, and until the pinching portion61B completely or generally completely passes through the holding bore57 on to a rear side of the panel. In this mounted state, laterallyouter end portions of the pinching portion 61A engage with a surface ofthe panel, while the turned-back portion 61B-2 of the pinching portion61B engages with an edge or an inner edge of the holding bore 57.Accordingly, the fixing clamp 48 is mounted stably in the panel. On theother hand, it is carried out smoothly to insert the fixing clamp 48 inthe holding bore 57 and it is possible to pull the fixing clamp 48 outof the holding bore 57.

As shown in FIGS. 5 and 7, closing members 66, 66 are mounted to bothends of the piping unit 13, specifically to the connectors 16, 16 onboth ends of the piping unit 13, before the piping unit 13 is assembledin the motor vehicle body.

The closing member 66 has a flange portion 68, a large diameter portion70 continued from the flange portion 68, and a closing shaft 72 that hasa smaller diameter than the large diameter portion 70. While the closingmember 66 is plugged in the connector 16, the O-rings 22, 22 or the bush24 and the O-rings 22, 22 as sealing member are fitted air-tightly on anouter peripheral surface of the closing shaft 72 and thereby an openingor through-bore of the connector 16 for connecting with the mating pipe10 is closed.

On each of a pair of the connectors 16, 16, a checker member (here, madeof resin) 74 is mounted or installed before the piping unit 13 isassembled in the motor vehicle.

The checker member 74 is configured to be disengaged or removed from theconnector 16 when the connector 16 is connected with the mating pipe 10correctly. Therefore, correct connection of the connector 16 and themating pipe 10 may be verified by removing the checker member 74 orcollecting the checker member 74.

FIGS. 6 and 8 show a construction of the checker member 74 concretely.

As shown in the figures, the checker member 74 has a base portion 76 ofrectangular or oblong shape. The base portion 76 is formed integrallywith a circular knob 78.

The base portion 76 further has a pair of resilient arms 79, 79 on theother side of the knob 78. The resilient arms 79, 79 extend insemiannular shape or arcuate shape as a whole, and are formed integrallywith stop claws 80, 80 that are directed inwardly facing each other onend portions of the resilient arms 79, 79.

Each of the stop claws 80 includes front and rear surfaces, namely frontand rear surfaces in an inserting direction of the mating pipe 10, in aradially inner end, that define slant surfaces 82, 82. And, as shown inFIG. 8, each of the stop claws 80 further includes one circumferentialsurface that defines a slant surface 84.

The base portion 76 is further formed integrally with clip portions 86,88 on rear and front end portions thereof (left end portion and rightend portion in FIG. 6), on a side of the stop claws 80. The clipportions 86, 88 clip the large-diameter retainer holding portion 26 ofthe connector 16 from front and rear sides.

Here, one clip portion 86 is formed with a dent 90.

The checker member 74 functions in a following manner.

FIG. 8 shows a state that the checker member 74 is mounted or installedon the connector 16.

When the checker member 74 is mounted on the connector 16, the pair ofstop claws 80, 80 of the checker member 74 enter in the windows 30 ofthe connector body 18 while engaging with circumferential edge portionsof the windows 30. Under this engaging force, the checker member 74 isfixed and retained on the connector 16.

At that time, as shown in FIG. 7, the pair of clip portions 86, 88 clipthe large diameter retainer holding portion 26 of the connector body 18from front and rear sides, namely in the axial direction, while latchingthe dent 90 formed on the one clip portion 86 onto a trailing end (aproximal end or axially outer end) of the retainer holding portion 26.

When the mating pipe 10 is inserted within the connector 16 in thisstate, as shown in FIGS. 9 (A) and 9 (B), the engaging projection 12abuts with the slant surfaces 82, 82 of the pair of the stop claws 80,80, and thereby the pair of the resilient arms 79, 79 and the stop claws80, 80 are forcibly widened or spread apart. This state is shown in FIG.9 (C).

When go into this state, the slant surfaces 84, 84 of the stop orlatching claws 80, 80 are lodged on circumferential edge portions (forexample, outer ends of the edge portions) of the window 30, namely,engagement (stop engagement) of the pair of the stop claws 80, 80 withthe circumferential edge portions of the window 30 is released orcancelled. And, the checker member 74 is easily removed from theconnector 16 by pulling down (downwardly in FIG. 9 (D)) the knob 78 byhand (refer to FIG. 9 (D)).

The pair of the stop claws 80, 80 of the checker member 74 are locatedjust in the positions (axial positions) of the engaging recessedportions 34, 34 of the retainer 20. Therefore, removal of the checkermember 74 from the connector 16 indicates that the engaging projection12 of the mating pipe 10 is surely fitted in the engaging recessedportions 34, 34 of the retainer 20.

Namely, this indicates that the mating pipe 10 is surely connected tothe connector 16.

EXAMPLE

A test is conducted in a following procedure with respect to examplesand comparison examples of the resin tube 14 in order to clarify arelationship between the bending breaking resistance and a ratio of anouter diameter (od)/a wall-thickness (t) (wall-thickness ratio) in theresin tube 14.

Here, examples and comparison examples of resin tube 14 have the sameouter diameter (od) of 4 mm (except for comparison example No. 6), butvaried wall-thickness (t). Each of them is bent at 90°, while being heldat both ends by the fixing clamps 48, 48.

Then, the fixing clamps 48, 48 are rearranged a shorter distance aparton each of them to hold it. And, each of them is bent again at 90° in asimilar way, while being held by the fixing clamps 48, 48.

The above is repeated until the resin tube is broken (buckled orkinked), and searched is a minimum bend R (radius or curvature radius)that does not cause breakage with respect to each of the samples and thecomparison samples. Here, the bend R is a curvature radius at an insideof a bent portion of the outer layer (refer to reference character R inFIG. 1 (B)).

At the same time, connector force-fit test is conducted to confirmforce-fit workability (insertability) for the connector 16.

The resin tube is preliminary diametrically enlarged at an end portionand then the connector 16 is force-fitted in the end portion of theresin tube.

The test results are shown in Table 1 and FIG. 10.

In the Table 1, Nos. 2 to 4 are examples with respect to the presentinvention, and No. 1, No. 5 and No. 6 are comparison examples.

The examples and the comparison examples have the same multilayeredconstruction as the resin tube 14, except for dimensions (refer to FIG.5 (B)). Regarding the examples and comparison examples, an “outerdiameter” indicates the outer diameter of a PA outer layer, and a“wall-thickness” indicates the wall-thickness of an ETFE inner layer(innermost layer) and the PA outer layer. TABLE 1 Construction of layersWall- PA Outer thick- ETFE outer Ratio to Bend Insert- diameter nessinnermost layer wall- R ability No. (mm) (mm) layer(mm) (mm) thickness(mm) *1) 1 4 0.25 0.1 0.15 16 30 ∘ 2 4 0.5 0.13 0.37 8 10 ∘ 3 4 0.75 0.20.55 5.3 8 ∘ 4 4 1 0.27 0.73 4 7 ∘ 5 4 1.5 0.4 1.1 2.7 5 x 6 8 1 8 50 ∘Note *1):With regard to “insertability”, a mark “∘” means that a connector isfavorably force-fitted in a resin tube, and a mark “x” means that theconnector is hard to be force-fitted in the resin tube.

As understood from the results, with decrease of the ratio of the outerdiameter (od) to the wall-thickness (t) (the outer diameter (od)/thewall-thickness (t)), the value of bend R in the table 1 becomes small,namely, a resin tube becomes hard to be broken.

However, in case where the ratio of the outer diameter (od) to thewall-thickness (t) is too small, insertability of the connector 16 isdeteriorated.

It is understood from the result of Table 1 and FIG. 10, in view ofresistance to breakage of the resin tube and insertability of theconnector 16, the ratio of outer diameter (od) to wall thickness (t) issuitably in the range of 4 to 8.

The comparison example No. 6 satisfies the condition of the ratio of theouter diameter (od) to the wall thickness (t) in the range of 4 to 8,but has a large value of 50 relative to bend R. Namely, the comparisonexample No. 6 is broken (buckled) very easily.

This result is explained as follows. When a resin tube is bent atcertain bend R, namely at certain curvature radius, the larger outerdiameter the resin tube has, the more sharply outer and inner peripheralsides are bent, specifically the more sharply the inner peripheral sideis bent. Further, due to the large diameter, resistance to breakage ofthe comparison example No. 6 is lowered.

According to the above embodiment, the connector 16 allows an operatorto easily connect the mating pipe 10 and the piping unit 13 with alittle labor, and the resin tube 14 may be favorably prevented frombeing broken when a bending force is exerted on the resin tube 14, bylimiting the ratio of the outer diameter (od) to the wall-thickness (t)within the range of 4 to 8. And, thereby the resin tube 14 may be easilyassembled in a motor vehicle body while bending the resin tube 14.

And, according to the present embodiment, the checker member 74 ismounted or installed to the connector 16 before the mating pipe 10 isinserted in the connector 16. Thereby it is not required to verifyconnection or connecting status of the connector 16 with the mating pipe10 visually or by visual observation during assembly of the piping unit13. In case where connecting work is done for a place beyond anoperator's view such as a remote part in the motor vehicle body, theoperator can easily verify a correct connection by removing orcollecting the checker member 74.

According to the present embodiment, the closing member 66 is mounted onor attached to a connecting opening or through-bore of the connector 16so as to close the connecting opening or through-bore before theconnector 16 is connected to the mating pipe 10. Thereby it may befavorably prevented that dust or other foreign particle enters insidethe resin tube 14 through the connector 16.

The connectors 16 and the closing members 66 may be attached or mountedto both end portions of the resin tube 14. When one closing member 66 isremoved from one of the connectors 16 on both ends of the resin tube 14and only the other closing member 66 is left on the other of theconnectors 16, the operator can easily verify whether there is leakageat a joint area (connecting area) between the connector 16 and the resintube 14 or in the connector 16 and the resin tube 14 by exerting apressure inside the resin tube 14 through an open end of the oneconnector 16.

Further, in the present embodiment, a small diameter resin tube withouter diameter or outer diameter (od) up to 6 mm is adapted for theresin tube 14 of the piping unit 13. When such small diameter tube isused for piping of a returnless fuel system, a flow velocity oftransporting a fuel does not become slow. This restrains a temperatureincrease of a fuel fluid inside the resin tube 14. Therefore, the resintube 14 is suitably adapted for piping of such returnless fuel system.

A connector, which has a retainer that is deformable resiliently in aradial direction, may be adapted for being attached to each of (or oneof) both end portions of the resin tube 14. The retainer may beconfigured separately from, unitary with or integrally with a connectorbody. In the connector that is used in embodiments according to thepresent invention, when the mating pipe 10 is inserted in the connectorbody, the retainer is pushed by the engaging projection 12 of the matingpipe 10, is deformed once in a radial direction (for example, deformedso as to expand in the radial direction), then is returned resilientlyto its original shape to engage with the engaging projection 12 of themating pipe 10. As a result, the connector body is securely fixed withthe mating pipe 10 in an axial direction. For example, may be adaptedthe connector 300 shown in FIG. 14 wherein the retainer 302 is mountedor incorporated in the retainer holding portion 304, for example, as aunit. Or, may be also adapted the connector 400 shown in FIG. 17 whereinthe retainer 402 is allowed to be pushed with respect to the retainerholding portion 404 only when the mating pipe 202 or the mating pipe 10is completely inserted in the connector 400. When the connector 300 orthe connector 400 is adapted, the connecting portion 312 or theconnecting portion 414 is configured suitably to be fitted in the resintube 14 (for example, as a force-fit portion).

Although the preferred embodiments have been described above, these areonly some of embodiments of the present invention. The present inventionmay be constructed and embodied in various configurations and modeswithin the scope of the present invention.

1. A piping unit arranged between an engine and a fuel tank fortransporting a fuel, comprising: a resin tube as an essential elementfor the piping unit, a connector attached to an end portion of the resintube for connecting the resin tube to a mating pipe, the connectorhaving a connector body including a retainer holding portion on one endof the connector body along an axial direction and a tube connectingportion on the other end of the connector body along the axial directionfor connecting to the resin tube, a retainer held in or on the retainerholding portion for engaging with the mating pipe to securely fix theconnector body in an axial direction, and a sealing member contactingair tightly with an outer peripheral surface of the mating pipe toprovide a seal between the connector body and the mating pipe, whereinthe resin tube has a multilayered construction including an inner fuelbarrier layer and an outer layer made of polyamide covered further witha protective layer on an outer peripheral surface of the outer layer,the resin tube inside the protective layer has a small outer diameter(od) up to 6 mm and a wall-thickness (t), a ratio of the outer diameter(od) of the resin tube/the wall thickness (t) of the resin tube is in arange of 4 to
 8. 2. The piping unit as set forth in claim 1, wherein theretainer holding portion is in a form of a socket shape.
 3. The pipingunit as set forth in claim 1, wherein the fuel barrier layer is made ofethylene-tetrafluoroethylene.
 4. The piping unit as set forth in claim1, wherein a main constituent of the fuel barrier layer is a materialselected from a group consisting of ethylene-tetrafluoroethylene,thermoplastic polyester elastomer, polybutylene terephtharate,polybutylene naphthalate, polyphenylene sulfide, polyethylene,polypropylene, polyvinylidene fluoride, and polyethylene vinyl alcohol.5. The piping unit as set forth in claim 1, wherein the resin tube isattached to the connectors at both end portions of the resin tube byforce-fitting or solvent welding.
 6. The piping unit as set forth inclaim 1, wherein a checker member is formed or mounted in or on theconnector, the checker member is configured disengageable from theconnector when the mating pipe is connected to the connector correctly.7. The piping unit as set forth in claim 1, wherein a closing member ismounted in the connector for closing a connecting opening through whichthe mating pipe is inserted in the connector before the mating pipe isconnected to the connector.
 8. The piping unit as set forth in claim 1,wherein the piping unit is used for piping in a returnless fuel systemin which the fuel is supplied from the fuel tank to an injector of theengine, but is not returned from the injector to the fuel tank.